Prostate Cancer Treatment May Up Colon Cancer Risk

NEW YORK (Reuters Health) - Men who opt for hormone-blocking therapy to treat prostate cancer may be increasing their risk of developing colon cancer, hints a study published this week in the Journal of the National Cancer Institute.

So-called "androgen deprivation therapy," or ADT, suppresses production of the male hormone testosterone, which helps drive the growth of prostate cancer. ADT is widely used to treat prostate cancer, despite increasing recognition that it carries serious potential risks, including diabetes and obesity, which are known risk factors for colon cancer.

Just last month, the U.S. Food and Drug Administration ruled that certain hormone treatments for prostate cancer must carry new warnings about an increased risk of diabetes and heart problems. Those medications include Lupron, Zoladex, Trelstar, and Eligard.

Studies in animals have also suggested that male hormones may protect against the development of colon cancer by suppressing signals the cancer cells need to grow, the authors write.

So it is "conceivable" that suppressing the hormones might increase the risk of colon cancer, Dr. Vahakn Shahinian, of the University of Michigan, Ann Arbor, told Reuters Health.

He and his colleagues looked for ties between the use of ADT and colon cancer in more than 100,000 older men who were diagnosed with prostate cancer between 1993 and 2002.

The men received ADT either in the form of drugs or surgery to remove the testicles, which produce more than 90 percent of the body's male hormones (androgens), including testosterone. Most opted for drugs. They were followed through 2004.

The researchers found that men who received ADT, relative to those who did not, had a 30 to 40 percent increased risk of developing colon cancer during the follow-up period.

The analysis took into account factors such as existing obesity and socio-economic environment that might influence colon cancer risk.

And the longer the men took ADT, the greater their risk of developing colon cancer, suggesting a "dose-response" relationship.

It's important to note, however, that this was an "observational" study, which can only point to a link (or lack thereof) between two variables - in this case, ADT and colon cancer. This type of study cannot prove cause-and-effect.

And, Shahinian told Reuters Health, the absolute risk of colon cancer in all of the men was small; over 5 years, it was just 2.2 percent for men on androgen-blocking drugs and 3.2 percent in those who had surgery, compared with 1.8 percent in the men who did not receive ADT.

Nevertheless, the impact may be large given that hundreds of thousands of men are on ADT for prostate cancer, the researchers note in their report.

"When considering starting ADT, men should carefully weigh the risks versus benefits of the therapy," advised Shahinian in an e-mail. "Since the risk of colorectal cancer is small, men shouldn't hesitate to use ADT when it is likely to be clearly beneficial for them," he added.

Dr. Jennifer H. Lin, of Brigham and Women's Hospital in Boston, and co-author of a commentary on the study, told Reuters Health that several simple measures may help prevent the development of colon cancer and "help to counter some of the drawbacks of ADT."

These include routine screening for colorectal cancer and adopting a healthy lifestyle, complete with plenty of physical activity.

Shahinian and colleagues say their findings have potential broader implications, beyond prostate cancer, given that testosterone deficiency is now recognized to be relatively common in the general population of men, affecting perhaps as many as 2.4 million men in the U.S., or about 2 percent of adult males.

Testosterone deficiency is generally considered to be a testosterone level below 3.2 nanograms per liter of blood, which is about half the "low-normal" level for a middle-aged man. (See Reuters Health story June 16, 2010.)

Whether these men are also at increased risk for colon cancer will need to be explored further, the researchers emphasize. In addition, they think future studies of testosterone replacement therapies should look for increased colon cancer cases to provide more data to analyze.